Using NCEP reanalysis data, conventional weather data and Doppler radar data, the characteristics of the synoptic and mesoscale meteorological background are analyzed for a torrential rainfall over Xiaoshipeng Town of Yingkou City in Liaoning Province. The results show that the Pacific subtropical high extends to the west, a strong tropical storm Muifa moves to the northwest after it lands; the southwest airflow at the east side of the tropical storm transports abundant water vapor to Liaoning, and the weak cold air of Baikal Lake moves south along the ridge before the northwest flow impacts Liaoning. Besides the existence of a deep wet layer, a narrow CAPE zone and a relative weak vertical wind sheer are beneficial to severe convective rainfall. The new mesoscale convective cells are generated continuously during the heavy rainfall. There exists a maximum wind speed zone of 24 m·s-1 in the lower layer and a strong radar echo with 35 dBz above 5 km. And the variation of the low level southwest jet is in step with the variation of rainfall intensity. The cyclonic convergence of the warm moist air in the mid low level triggers and strengthens convection. The nonstop generation of mesoscale severe convective cells and the water vapor transport from the low level northwest jet push the radar echo to above 40 dBz, lasting for more than 5 hours. In addition, the valley torrain has great influence on the torrential rain as well.